from The American Heritage® Dictionary of the English Language, 4th Edition

adj. Characterized by usually exaggerated predictions of or allusions to a disastrous outcome: "Stripped of its apocalyptic tone, what this amounts to is an advocacy of teaching names, dates and places by rote” ( Stefan Kanfer).

adj. Of a revelatory or prophetic nature.

from Wiktionary, Creative Commons Attribution/Share-Alike License

adj. Of or relating to an apocalypse:

adj. Portending a future apocalypse (disaster, devastation, or doom).

n. One who predicts apocalypse.

from the GNU version of the Collaborative International Dictionary of English

adj. Of or pertaining to a revelation, or, specifically, to the Revelation of St. John; containing, or of the nature of, a prophetic revelation.

The father of two, whose parish has the wide brew of amicable conditions, said his recommendation to people in apocalyptic circumstances is that 'they should not hurt anybody as well as cope as most appropriate they can'.

Those early teens were formative years, because reading A.S. Neill's "The last Man alive", a hilarious book about a teacher and some of his students being the last people on earth, at the age of thirteen woke my interest in apocalyptic SF stuff.